We should also keep a track of folks and vids of some 'custom' setups. I have my MadDad midpipes hanging around off my 135i, and was planning on slapping them on the 1///M. The HPA car is running an aftermarket midpipe on stock exhaust too (Berk IIRC) and I recall the guys commenting it sounded sweet.
PS: That last clip of the Akra on the street car is darn loud!
2011 BMW E82 1///M: AW, all options; Renntech, Akrapovic, Forge, P3, RevoZ CF bits, many mods
1988 BMW E30 M3: Hennarot, S14, stock
2016 Porsche 981 GT4: Guards Red, LWBS, SC, full leather
1998 Porsche 993 C4S: Zenith Blue, last aircooled widebody, Bilstein PSS10, Fister II + Fabspeed exhaust
2008 Audi B7 RS 4: Sprint Blue, Audi Exclusive Euro Bucket Interior, Premium+Titanium, many mods